Metallizing apparatus



July 11, 1957 c. G. FOSSATI 3,330,938

METALLIZING APPARATUS Filed March 14, 1966 2 Sheets-$heet l INVENTOR. CHARLES G. F ossA'n Afforw ra' July 11, 1967 c FOSSATI 3,339,938

METALLI Z ING APPARATUS Filed March 14, 1966 2 Sheets-Sheet 2 FIG. 5

INVENTOR CHARLES G. FOSSATI ATTORNEYS 3,330,938 METALLIZING APPARATUS Charles G. Fossati, 11646 Whittier Ave., Detroit, Mich. 48224 Filed Mar. 14, 1966, Ser. No. 543,444 2 Claims. (Cl. 219-275) This application is a continuation-in-part of application Ser. No. 382,182, filed July 13, 1964, now abandoned.

The present invention relates to the application of metal coatings by thermal evaporation and more particularly to the construction of an improved filament and evaporant for use in such thermal evaporation metallizing processes.

The improved filament and evaporant is used in the process of coating the surfaces of various articles by vaporizing a metal element in a vacuumized chamber containing the article to be coated. The process is generally carried out by electrically heating a filament constructed of tungsten or similar material within the chamber and by positioning the metal to be evaporated in contact with the filament so that it will be heated thereby to a point of evaporation.

Heretofore the filaments used for carrying out this process have generally been in the form of lengths of either straight or coiled wire connected across spaced electrical terminals. The evaporants, that is, the metal to be evaporated to coat the article, have heretofore been in the form of a plurality of wire loops or small clips fastened or hung at spaced points along the filament. In some cases, straight pieces of wire may have been inserted within a coil filament.

Such a filament and evaporant construction has several disadvantages which are overcome by the construction of the present invention. First, the crimping of the evaporant clips or wires over the filament tends to weaken the filament and thereby to shorten filament life. Further, the time and labor required to hang the evaporant, one clip at a time, makes the cost of carrying out the process quite expensive. Also, a filament loaded in this particular manner tends to heat from the center towards the ends where the filament is secured to the terminal posts because the mass of the terminal posts tends tomaintain the ends of the filament at a lower temperature than the center. Uneven heating of the filament tends to cause uneven evaporation of the evaporant resulting in dark imperfect spots on the article to be coated. Also, molten metal tends to collect and drop from the ends of each of the evaporant wires or clips which also results in imperfect coating as well as wasted materials.

When a coil-type filament is used, such as shown in US. Patent No. 2,384,500, it is difficult and time-consuming to insert the evaporant within the coils. Other special types of evaporant elements intended to be laid upon a substantially fiat or slightly dish-shaped span of filament, such as shown in US. Patent No. 2,693,167, are expensive and produce excessive dripping and loss of evaporant metal.

The present invention provides a filament construction in the form of an elongated strip of tungsten or similar material shaped to provide a cradle or trough V-shaped when viewed from the end. The evaporant in the form of a straight length of wire or ribbon is carried in the V- shaped cradle or trough formed by the filament. The length of evaporant wire or ribbon laying across the filament tends to electrically short the filament causing it to heat up from each end toward the center. This assures complete evaporation of the evaporant at the ends of the filament since the heat in this area is sufficiently high to prevent the metal from remaining in the molten state long enough to cause poor coating. Since the evaporant melts towards the center, the electrical short is auto- Patented July 11, 1967 matically reduced until its is completely eliminated and all of the evaporant is evaporated.

Also, with the filament being V-shaped, the straight wire or ribbon evaporant tends to be spaced above the apex of the V a distance depending on the diameter of the evaporant wire or thickness of ribbon and the angle of the V. These can be calculated such that the melting evaporant will initially wet the filament to the maximum extent but will not drip off, resulting in the most effective, uniform, and rapid vaporization.

Further, it has been found that by laying the wire or ribbon evaporant across the filament, a more intimate contact is made with the filament than is achieved when clips or the like are hung from the filament. This more intimate contact in combination with the particular manner in which the evaporant is heated from the ends towards the center, produces a superior melting of the filament and evaporation of the evaporant.

The particular manner in which the evaporant is carried by the filament also substantially reduces the time required to load evaporants, and the features of filament construction of my invention help to retain the evaporant securely against both lateral and longitudinal dislodgment from the filament after loading.

Furthermore, since it is not necessary to crimp a num ber of individual clips to the filament, the particular manner of loading greatly increases filament life through the reduction of abuse to the filament.

It is an object then of the present invention to increase the life of filaments for vacuum metallizing processes by providing an improved construction for such filaments in which the evaporant in the form of a link or strand of wire or ribbon is carried in a V-shaped cradle or trough formed by the filament.

It is another object of the present invention to improve the coating of objects by metal evaporation by providing a filament and evaporant combination constructed to produce heating of the evaporant from the ends of the filament toward the center.

It is another object of the present invention to more uniformly coat objects by metal evaporation by providing an improved filament and evaporant construction operable to reduce the amount of molten metal tending to fall from the evaporant.

It is yet another object of the present invention to facilitate loading of filaments in thermal evaporation rnetallizin-g processes by providing an improved filament and evaporant construction in which the evaporant in the form of a straight length of wire or ribbon is carried in a V-shaped trough or cradle in the filament.

It is a further object of the invention to solve difiiculties in the use of metallizing processes by providing a specially constructed filament capable of retaining a simple straight wire or ribbon evaporant against dislodgment from the filament while enhancing filament wetting by the initially melted evaporant.

Still further objects and advantages of the present invention will readily occur to one skilled in the art to which the invention pertains upon reference to the following drawings in which like reference characters refer to like parts throughout the several views and in which FIG. 1 is a perspective view, partially broken away, of one type of thermal evaporation apparatus employing the filament and evaporant construction of the present invention.

2 is a perspective view of a filament and evaporant construction of the present invention.

FIG. 3 is an end view of the combination shown in FIG. 2. I

FIG. 4 is a side elevational view of the combination shown in FIG. 2.

Now referring to the drawings for a more detailed description of the present invention, a suitable apparatus for utilizing the improved filament and evaporant of the present invention is illustrated in FIG. 1 as comprising a supporting base upon which is mounted a housing 12. The

housing 12 may be in the form of a bell jar or the like having a dome-like top portion 14 and an annular flange 16 adapted to rest on the supporting base 10. A chamber 18 is defined by the top section 14 and an article 20 to be coated is carried on a support 22 positioned within the chamber 18.

A pair of upright terminal supports 24 are positioned within the chamber 18 and are mounted upon the supporting base 10. An electric filament 26 is carried by the supports 24 in a substantially horizontal position. An evaporant wire 28 is carried by the filament 26 in a manner which will be more clearly described below.

The chamber 18 is preferably evacuated of air through an outlet pipe 30 to produce a high vacuum therein by any suitable vacuum creating means (not shown).

The filament 26 is preferably constructed of tungsten, tantalum, molybdenum or columbian as is Well known in the art preferably comprising several strands of wire of such material woven together in the conventional manner. The filament 26 as can best be seen in FIGS. 2 and 4, is bentat a plurality of substantially equally spaced points along the length to form a series of alternate and spaced peaks 32 and V-shaped valleys 34. The filament 26 is preferably formed at each end by providing a substantially vertically extending portion 36 bent respectively upwardly from a valley 34. The ends are then bent again to provide substantially axially extending end portions 38. As can best be seen in FIG. 2, the filament 26 is bent alternately in opposite directions outwardly and angularly with respect to a vertical plane containing the longitudinal axis of the filament 26 and the apex portion of each V- shaped valley 34 so that alternate peaks 32 and adjacent portions of valleys 34 define substantially planar sides of a trough or cradle which is V-shaped in lateral cross section.

The evaporant 28 preferably comprises an elongated ribbon, straight strip or wire of suitable material such as aluminum or the like and is carried and effectively retained within the cradle or trough formed by the filament '26. The vertically extending portions 36 of the filament 26 prevent the evaporant 28 from falling or being longitudinally dislodged from the ends of filament 26,

while the V-shape of the filament prevents the wire from rolling off of the filament.

Although it has been preferred to illustrate the single improved filament and evaporant construction of the present invention in the particular apparatus shown in FIG. 1, it is to be understood that more commonly a plurality of filaments and evaporants are arranged to be disposed within the vacuumized chamber 18. Similarly, a plurality of articles 20 may be positioned within the chamber 18 to be coated.

In carrying out the process of coating the article 20 by metal evaporation, the chamber 1 8 is vacuumized after the article 20 has been placed within it and an evaporant 28 has been positioned in the cradle or trough formed by the filament 26. With a high vacuum in the chamber 18 the filament 26 is energized through the terminal supports 24 to cause the filament 26 to become electrically heated. In the particular filament and evaporant construction of the present invention, the evaporant 28 tends to produce a short circuit across the filament 26 so that a substantial portion of the electrical energy initially flows through the end portions 3 8 and through evaporant 28 bypassing the remainder of the filament 26. This produces the greatest heating of the filament 26 in the area of the end portions 28 and tends to evaporate the evaporant 28 from the ends toward the middle. As the ends of the evaporant 28 are evaporated to begin coating of the article 20, the length of the evaporant 28 is shortened and more of the filament 26 becomes heated. In this way the evaporant 28 will be continued to be heated by the filament 26 and to evaporate from each end toward the center to produce a superior coating as heretofore pointed out.

FIG. 5 illustrates an intermediate step in the forming of the filament 26 of FIG. 2. Wire filament 26 may be shaped into a corrugated formation as shown to form the plurality of V-shaped peaks 32. The wire is then bent upward along a longitudinal center line C, so that V- shaped valleys 34 will be along the line of intersection of two angularly disposed planes A and B as shown in FIG. 3. Theends will then be bent upward to make the portions 26 lying in the medial plane M and then outwardly to form the portions 38 to connect to the terminals 24 of FIG. 1.

FIG. 6 illustrates an alternate intermediate step in the forming of the filament 26 of FIG. 2. The wire filament 26 is shaped into a corrugated formation as shown to form a plurality of V-shaped peaks 32 and V-shaped valleys 34, plus the upstanding portions 36 with the projecting terminal ends 38. Then alternate peaks 32 are bent to opposite sides (as viewed from the end) to make them lie in the angularly disposed planes A and B of FIG. 3, leaving the V-shaped valleys 34 in the line of intersection C and the end portions 36, 38 disposed in the medial plane M.

Either way, the end result is the same.

The V-shaped valleys 34 are preferably formed to a substantially sharp break angle, so that, as seen in the enlarged view of FIG. 7, when the evaporant ribbon 28 (dotted line) wire 28 (solid line) is laid in place, there will be a small gap 40 between the evaporant and the interior apex of the V. The vertical extent of this gap will be dependent on the angle of the break or V and the diameter of the evaporant wire 28 or thickness of the ribbon 28. The present construction permits the calculation of these dimensions, relative to the heat which will be electrically produced in the particular filament used, so that the initially melted evaporant will wet downwardly along the filament but will not drip. off before it becomes vaporized. In FIG. 8, it will be seen that the gap 40 is larger than the gap 40 of FIG. 7 due to the smaller V angle. The evaporant 28, riding higher in the filament, is thus given a longer Wetting" opportunity. Also, a larger diameter evaporant wire 28".or thicker ribbon 28", shown in dotted lines in FIG. 8, will ride higher in the filament, producing a longer wetting opportunity.

Some evaporant materials melt at different rates than others, so both their diameters or thicknesses and the filament V angle can be varied to produce the most effective use of the evaporant with the least or even no waste.

It is apparent that the particular filament and evaporant construction of the present invention permits ready loading of the filament since the evaporant is simply dropped into the cradle or trough formed by the filament 26. There is no need to load a plurality of evaporants at spaced points along the filament. Further, the particular filament and evaporant construction of the present invention leads to greatly increased filament life since the evaporant 28 merely rests within the filament 26 and is in no way secured or crimped thereto. The evaporant 28 is provided With just two end portions so that potential collecting and dropping of molten evaporant material is substantially reduced to produce a more perfect coating of the article 28 and substantially reduce wasted evaporant material.

It is also apparent that although I have described but a single embodiment of my invention, many changes and modifications can be made therein without departing from the spirit of the invention as expressed by the scope of the appended claims.

I claim:

1. In a metallizing apparatus, a filament adapted to be electrically heated, and an evaporant carried by said filament,

(a) said filament comprising a length of wire formed to lie in two longitudinal intersecting planes with a plurality of portions of the wire lying in each plane, each portion of the wire having diverging legs extending from a point on the plane toward the line of intersection of said planes, the portions in each plane meeting at the intersection of the planes with the ends of the legs in the other plane, whereby to define a longitudinal cradle having a. V-shape when viewed from the end thereof,

(b) said evaporant comprising an elongated element carried in said cradle,

References Cited UNITED STATES PATENTS 2,693,167 11/1954 Fox et a1. 11849 RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner. C. L. ALBRITTON, Assistant Examiner. 

1. IN A METALLIZING APPARATUS, A FILAMENT ADAPTED TO BE ELECTRICALLY HEATED, AND AN EVAPORANT CARRIED BY SAID FILAMENT, (A) SAID FILAMENT COMPRISING A LENGTH OF WIRE FORMED TO LIE IN A TWO LONGITUDINAL INTERSECTING PLANES WITH A PLURALITY OF PORTIONS OF THE WIRE LYING IN EACH PLANE, EACH PORTION OF THE WIRE HAVING DIVERGING LEGS EXTENDING FROM A POINT ON THE PLANE TOWARD THE LINE OF INTERECTION OF SAID PLANES, THE PORTIONS IN EACH PLANE MEETING AT THE INTERSECTION OF THE PLANES WITH THE ENDS OF THE LEGS IN THE OTHER PLANE, WHEREBY TO DEFINE A LONGITUDINAL CRADLE HAVING A V-SHAPE WHEN VIEWED FROM THE END THEREOF, (B) SAID EVAPORANT COMPRISING AN ELONGATED ELEMENT CARRIED IN SAID CRADLE, (C) SAID FILAMENT HAVING PORTIONS PROVIDED AT OPPOSITE ENDS OF THE EVAPORATANT TO RETAIN SAME AGAINST LONGITUDINAL DISPLACEMENT FROM SAID CRADLE. 